Effects of interphase formation on the modulus and stress concentration factor of fiber-reinforced thermosetting-matrix composites

Experimental and theoretical studies in the literature have shown that a fiber surface perturbs its surrounding polymer to create a three-dimensional interphase zone with property gradients. Micromechanical stress analysis and evaluation of the effective properties of composites need the interphase material properties as input information. Since relatively scant information is available on the prediction of interphase formation as function of processing conditions, current micromechanical analyses have resorted to using assumed interphase property profiles. In this paper, a thermodynamic model for interphase formation is adopted to predict the interphase material properties, which, in turn, are used in the finite element analysis of overall composite properties. Relevant numerical results are presented for the first time where two major composite properties, modulus and stress concentration factor, are directly linked to the interphase formation parameters without assumed structures or properties of the interphase. The results provide guidelines for selecting material components and processing parameters to achieve desired overall composite properties.